In the conventional designs for LTE systems, downlink reception at a User Equipment (UE) is facilitated by channel estimation and symbol detection based on Cell specific Reference Signal (CRS). Since the CRS is a common reference signal, operations such as downlink data transmission power allocating and precoding at a base station (eNB) side need to be signaled to the UE such that the channel estimation and symbol demodulation can be performed at the UE side. However, this causes some inconvenience for multi-user MIMO scheduling and power allocation.
In discussion of technical researches and standards for IMT-Advanced (e.g., LTE-Advanced) technology, a beam-forming technique is introduced, in which a UE uses a dedicated DMRS for channel estimation and symbol detection and the same precoding operation is performed on both user data and the DMRS to improve the downlink transmission performance.
The use of DMRS, which is subjected to the same operations as the data, makes the power allocation, precoding and scheduling for the UE more flexible at the base station. A certain offset is maintained between the power of the downlink data and the power of DMRS, such that the base station does not need to signal power allocation information. As for LTE/LTE-Advanced system, a certain offset is maintained between the power spectral density of data and the power spectral density of DMRS. In a DMRS design, however, there are a plurality of multiplexing approaches such as Frequency Division Multiplexing (FDM) and Code Division Multiplexing (CDM), such that it is difficult to maintain a fixed offset between the power of DMRS and the power of downlink data. Thus, the base station is still required to signal to the UE a power ratio between the DMRS and the downlink data, which causes a lot of inconveniences for multi-user power allocation in a Multi-User Multiple Input Multiple Output (MU-MIMO) mode.
Additionally, in order to realize Single User Multiple Input Multiple Output (SU-MIMO) and MU-MIMO, the use of a dedicated DMRS makes the system overhead for DMRS vary with the change in the number of layers multiplexed on channel resources. Thus, for different numbers of the multiplexed layers, it is required for the UE to obtain corresponding DMRS resource information and to employ a corresponding channel estimation approach. In the MU-MIMO operation mode, different DMRS resources used by the individual UEs will result in a large amount of combinations and an increased system signaling overhead on the downlink.
In light of the above, a solution for notification of DMRS resource allocation based on a fixed DMRS power offset is provided, capable of reducing signaling overhead for power allocation in the system, improving the efficiency of power amplifier and increasing the flexibility of system scheduling. A method of notifying antenna port resource allocation for DMRS is also provided.